This invention is directed to a circuit arrangement for regulating signals having differing amplitudes to maintain a signal at a predetermined constant level. The invention is useful with compact disc players and video tape recorders/players and other equipment having a rotating member. In such equipment signals having different levels are generated using photoelectric detectors and a pattern of lines, which is disposed on a member arranged to rotate in the proximity of the photoelectric detector, for example the perimeter of the rotor of a motor. The lines generate, by means of a light sensitive element, pulses which can be utilized for the commutation, speed and phase regulation of the drive motor. The pattern is composed of lines having a constant, narrow width arranged at equal spacing perpendicular to the direction of scanning. Some lines may be wider and serve to generate a switching signal used for the purpose of reversing the recording or, switching playback heads of a magnetic recording apparatus if the motor is the drum head cylinder motor of a video apparatus. However, the widths of the lines in the pattern are subject to tolerance variations. The photoelectric barrier also exhibits tolerance variations in its efficiency so that the peak values of the output signal are not constant. It is known to regulate the reference level R of the photoelectric barrier signal to a constant value. The amplitude of the signal pulses generated becomes independent of the coupling factor of the photoelectric barrier. However, with such a measure, differences in the ray trace of the photoelectric barrier, such as the focusing of the light beam, as well as deviations of the line width for different line patterns may still lead to differing signal amplitudes making it difficult to distinguish between two different levels.